Additive manufacturing (AM) enables to quickly create objects with complex shapes from a 3D CAD model. Among various technologies, the Fused Filament Fabrication (FFF) technique consists in depositing melted filaments of material layer upon layer to create the desired object. The use of semi-crystalline polymer is interesting as it can produce parts with worthy mechanical properties because of quality adhesion between the layers. Another advantage is its ability to be used on a wider range of temperature compared to amorphous polymers. The properties of semi-crystalline polymers are tailored by their crystallinity. Therefore getting more in depth grasp on their crystallization behavior is of primary importance for their use in FFF. The goal of this study is to understand the impact of the extrusion velocity, heating rate, substrate temperature and part geometry on crystallization. Two grades of commercial PolyPropylene (PP) are used. Both polymers have shown transcrystalline layers at the adhesion areas as well as at the free surface areas. Choosing a polymer with lower melting temperature allows more diffusion at the interface and thus longer transcrystalline layers. A layer's crystallinity will essentially depend on the height's at which it is printed, the number of strands in the layer and the strand's cross section. The results have shown that the neat filament initial crystallinity have a predominant impact of the phase crystallization. The rapid heating in FFF is shown to never completely erase the initial crystallinity of the polymer. Reducing the cooling rate consequently promote the formation of the beta phase as more time is allowed for growth. The crystallization behavior of PP in FFF is one of the issues that need to be better understood to enable its use. The achieved results should provide more insight on the printing parameters that can be used to obtain targeted properties.